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Determination of NO3- ions by colorimetric titration

Dosing principle

This method of colorimetric determination of nitrate ions can be applied to NO3- concentrations between 0.15 and 15 mg.L-1.

In an anhydrous medium, sulfosalicylic acid, created upon reaction of sulfuric acid with sodium salicylate, reacts with nitrates to form a mix of ortho- and para- sodium nitrosalicylate. In a basic environment, the nitrosalicylate anion is relased and its stable yellow color allows for a colorimetric titration at wavelength 415 nm.

Sodium salicylate + H2SO4 becomes Sulfosalicylic acid + NO3- becomes Nitrosalicylate anion

The addition of sodium and potassium double tartrate together with sodium hydroxide prevents the precipitation of calcium and magnesium salts.

Illustration of a standard range for the determination of nitrates. 12 beakers contain a yellow liquid with a more and more pronounced coloration.
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